Hallo all

I have a question as a new user to this program. So at the moment my boss asked me to do a floor area calculation which I find amusing.. the problem is very simple but asking my co-workers didn't help.

So when I'm doing the calculation, I made a mistake by klicking somewhere that I actually didnt want to include. How do I go back one step without losing all what I had already chose to calculate. I tried using Ctrl+Z and everything just went away.. so If there is any other way to go one step back please dont hesitate to share.. (struggling with a german keyboard here as well).

Thank you for your help in advance.

Cheers,
Maram